The present invention relates to an improved method of pumping and/or transporting viscous asphaltenic crude oils. More particularly, the present invention relates to the introduction into crude oils of an effective viscosity reducing amount of an oil soluble or oil-dispersible organic compound containing at least one oleophobic and hydrophobic fluoroaliphatic group.
Crude oils are complex mixtures comprising hydrocarbons of widely varying molecular weights, i.e. from the very simple low molecular weight species including methane, propane, octane and the like to those complex structures whose molecular weights approach 100,000. In addition, sulfur, oxygen and nitrogen containing compounds may characteristically be present. Further, the hydrocarbyl constituents may comprise saturated and unsaturated aliphatic species and those having aromatic character.
By a variety of fractionation procedures crude oils can be separated into various classes, the most common of which is boiling range. The mixtures which are in the lower boiling ranges generally consist of materials of relatively simple structures. The mixtures which are in the high boiling point ranges comprise substances which, with the exception of paraffins, are so complex that broad terms are applied to them such as resins and asphaltenes. Resins are poorly characterized but are known to be highly aromatic in character and are generally thought to be high molecular weight polynuclear aromatic hydrocarbons which melt over a wide, elevated temperature range.
Asphaltenes are aromatic-base hydrocarbons of amorphous structure. They are present in crude oils in the form of colloidally dispersed particles. The central part of the asphaltene micelle consists of high-molecular weight compounds surrounded and peptized by lower weight neutral resins and aromatic hydrocarbons. Asphaltene content generally increases with decreasing API gravity. The components of asphaltic materials are classified by their physical properties. Neutral resins are soluble in petroleum oils including C.sub.5 fractions while the asphaltenes are insoluble in light gasoline and petroleum ether. Asphaltenes are lyophobic with respect to low-molecular-weight paraffinic hydrocarbons and lyophilic with respect to aromatics and resins. The aromatics and resins peptize the asphaltene particle by adsorption on its surface, resulting in dispersion of the particle in the oil.
Any action of chemical, electrical or mechanical nature that depeptizes the asphaltene micelle may lead to flocculation and precipitation of the asphaltenes from the crude oil. The addition of low-surface-tension liquids--i.e. below 24 dyne/cm at 25.degree. C., such as gasoline, pentane, hexane, petroleum naphtha, etc. may precipitate asphaltenes. The addition of HCl during acidizing also tends to cause the formation of precipitated asphaltic-acid sludges. The flow of crude oil through porous media may also result in the precipitation of asphaltenes because of the neutralization of their charge by the streaming potential.
Asphaltene deposits are characteristically hard, brittle, dark black, dry solids, similar in appearance to coal and other bitumens. These deposits are very difficult to remove from a system because typical thermal methods of hot oil or water treatment are generally totally ineffective. The deposition of these materials also constricts or blocks the passage of crude oil causing reduced efficiency of production. Prevention or removal can be attempted chemically through the use of aromatic solvents, solvent accelerators, or the resinous components of crudes, or mechanically through tedious cutting operations.
Viscosity frequently limits the rate crude oil can be produced from a well. For example, in wells that are pumped by a sucker rod string, viscous drag by the crude oil on the string slows its free fall by gravity on the downstroke. On the upstroke, this drag also slows the string, decreases oil flow through the production tubing, and increases the power required to raise oil and rod string. In some instances where the oil is highly viscous, such as the Boscan field in Venezuela, the strength of the sucker rods limits the depth at which the pump can be operated. Alternatively, hydraulic pumps can be placed at the bottom of the well, but they must still overcome the high viscous drag that requires high power oil pressures and high pump horsepower.
The downhole pump usually provides the pressure required to pump the produced oil from the wellhead to surface gathering tanks. Where viscosity is high, this may require the use of extra strength wellhead equipment (packings, gaskets, heavy walled pipes and the like) to withstand the pressures required to move such viscous oil from wellhead to storage tank.
It has been proposed heretofore to reduce the viscosity of heavy crude oils prior to pumping by introducing low viscosity crude oils, white oil, kerosene or the like into the well bore to dilute or thin the produced crude. In rod pumped wells, it is common to surround the sucker rod string with an extra tubing. Low viscosity oil is pumped down this tubing so that the string is surrounded by lower viscosity oil. This added light oil then mixes with the viscous crude near the traveling valve of the pump to lighten and thin the column of crude oil being pumped from the well through the annulus formed by the inner and the production tubings of the well. Alternatively, low viscosity oil can be pumped down hollow sucker rods and the diluted crude oil produced through the annulus between the hollow rod string and the tubing.
The resulting produced crude has reduced viscosity and is more economically transported; However, these low viscosity diluents are expensive and not always available and have to be reclaimed from the diluted crude.
Another method for reducing the viscosity of asphaltic crudes is transporting them at elevated temperatures. This method however, is very expensive because the decrease in viscosity per degree temperature increase is very low.
Other approaches that have been suggested to reduce viscosity of asphaltic crudes include the use of aqueous surfactant solutions to form low viscosity oil in-water emulsion as shown in U.S. Pat. Nos. 3,943,954, 4,265,264, 4,429,554 and 4,239,052. Such emulsions generally contain a rather high percent water, for example 10-40% water, which must be removed. Removal is not always easy and yields large volumes of water contaminated with oil. High treating temperatures are required for separation of the water and this results in additional expenditures. Also, corrosion problems, freezing problems, and emulsion inversion into highly viscous water in oil emulsions problems may be associated with such aqueous emulsions, depending upon the nature of the field conditions, local climate, and the like.
It is thus an object of the present invention to obviate many of the drawbacks and deficiencies associated with the various prior art techniques that are presently used in the attempt to diminish the problems associated with the production, transportation and storage of crude oils. This object is achieved by employing oil soluble or oil-dispersible organic compounds having at least one oleophobic and hydrophobic fluoroaliphatic group which are viscosity reducers when dissolved or dispersed in such oils.